If you commute by bike every day it can become a labour. There are likely days when you look out the window and the weather says, "Take the bus dopey." But once you've strapped on all of the sweaty rain gear, covered your panniers with little shower caps and checked that all of your lights are blinking away, you're off. If you're actually out there doing it in those conditions then it's fair to assume that it probably it makes you happy.
Twenty years ago I rode across Canada and although I was none to enamoured with the persistently consistent landscape of Saskatchewan (not to mention the wind), that cycling introduction to this impressive country is one of my fondest memories. I'd have to concede that cycle touring in general has given me some of my most cherished memories.
I get a very similar pleasure these days from my daily commute. When I took my current job I readily admitted to my employer when he asked me how I liked the place that my favourite thing about it was my daily commute. I see aggressive and angry people from time to time riding bikes and I really don't know how they manage it. For me commuting is one of the best parts of my day. In my life 'Rosebud' was a bike!